As mobile devices have been increasingly developed, and the demand of such mobile devices has increased, the demand of secondary batteries has also sharply increased as an energy source for the mobile devices. One of the secondary batteries is a lithium secondary battery having high energy density, high operation voltage, and excellent storage and service life characteristics, which is now widely used as an energy source for various electronic products as well as various kinds of mobile devices
However, various combustible materials are contained in the lithium secondary battery. As a result, there is a possibility of danger in that the lithium secondary battery can be heated or exploded due to overcharge, overcurrent, or any other external physical impacts. In other words, the lithium secondary battery has low safety. Consequently, a protection circuit module (PCM) for effectively controlling the abnormality of the battery, such as overcharge, is mounted in the lithium secondary battery while the PCM is connected to a battery cell of the lithium secondary battery.
The PCM includes a field effect transistor (FET), which serves as a switching element for controlling electric current, a voltage detector, and passive elements such as a resistor and a capacitor. The PCM interrupts overcharge, overdischarge, overcurrent, short circuits, and reverse voltage of the battery to prevent the explosion or the overheating of the battery, the leakage of liquid from the battery, and the degradation of the charge and discharge characteristics of the battery, and to prevent the lowering of the electrical efficiency of the battery and the abnormal physicochemical behavior of the battery, thereby eliminating dangerous factors from the battery and increasing the service life of the battery.
Generally, the PCM is connected to the battery cell via a conductive nickel plate by welding or soldering. Specifically, the nickel plate is fixed to an electrode tap of the PCM by welding or soldering, and then the nickel plate is fixed to the electrode terminals of the battery cell by welding or soldering. In this way, the PCM is connected to the battery cell, whereby the battery pack is manufactured.
In this case, several welding or soldering operations are needed to manufacture the battery pack. However, these welding or soldering operations must be carried out with vary high accuracy since the structure of the secondary battery is small. As a result, the defective product rate is increased. Furthermore, the welding or soldering operations are added to the manufacturing process of the product, which increases the manufacturing costs of the product.
Consequently, a method of assembling the PCM and the battery cell without performing a spot welding or soldering process is seriously required. For this reason, much research on technologies for omitting the welding or soldering process has been carried out up to now.
For example, Korean Unexamined Patent Publication No. 2005-81175 discloses a battery pack including a PCM assembly, a cap housing for enclosing the PCM assembly, and electrode leads for electrical connection wherein a PCM block having a plurality of grooves, which communicate with the PCM assembly and the cap housing such that the electrode leads are exposed to the outside, is mounted to a battery cell.
Also, Korean Unexamined Patent Publication No. 2005-15314 discloses a battery pack wherein a printed circuit board (PCB) including a PCM and a protruding contact is mounted to a battery cell, and then the PCB is fixed to the battery cell by means of a fixing member.
The above-mentioned prior arts have advantages in that the welding or soldering process is omitted when the secondary battery is manufactured, whereby the assembly process of the battery is simplified, the number of components of the battery is decreased, and therefore, the manufacturing costs of the battery are reduced. However, the need of a battery pack that can be manufactured more economically and has increased manufacturing efficiency is still high.